This invention relates to polybenzazole ("PBZ") fibers and processes for making them.
Polybenzazole fibers are known to have good physical properties such as tensile strength (750 ksi) and tensile modulus (43 msi (heat treated fiber)). It is known to spin polybenzazole fibers from solutions of PBZ in various solvents (see Encyclopedia of Polymer Science and Technology, Vol. 11, pp 601-635). Coagulating PBZ fibers in cold temperatures is known to slightly enhance tensile properties of the fibers (U.S. Pat. No. 3,767,756). It is also known to slightly increase the tensile properties of spun PBO fiber by coagulating the fiber in a mixture of acid and water vs. coagulating the fiber in water alone. (Synthesis, Spinning, and Fiber Mechanical Properties of Poly(p-phenylenebenzobisoxazole) by Choe and Kim Macromolecules, vol. 14, 1981, pp. 920-924.)
PBZ fibers with ultra-high physical properties and a spinning process for creating them are needed to meet certain needs of the marketplace.